Science Graphic of the Week: 5.3 Million Years of Sea Level Change on One Cliff Face

5.3 million years of sea levels, beginning at top left and finishing at bottom right. (Rohling et al./Nature)

It’s not often that we think about deep time. Lucky to live for a century, humans flitter like mayflies across Earth’s surface, our own epoch an eyeblink in a planetary history that’s largely hidden from everyday consciousness.

And such is the sort of story told in the cliffs at Punta di Maita, Italy (photo below). Each band is a layer of seafloor sediment that accumulated long ago in 21,000-year orbital cycles, and was eventually pushed by tectonic activity into their current formation. They are time made macroscopic — and when microscopic fossils in the layers were analyzed by researchers from Australian National University, they told a climate tale stretching back 5.3 million years.

As described in an April 17 Nature study, the researchers used measurements of oxygen levels in plankton fossils from the Punta di Maiata formations to infer prehistoric water flows through the Straits of Gibraltar, which in turn reflect sea level changes caused by the melting or freezing of glaciers. The upshot: 5.3 million years of deep-sea temperature trends — graphed in the image above — which extend the deep-sea record by several million years and suggest that the current glacial period began 200,000 years earlier than traditionally thought.

That insight aside, the new method could lay a foundation for a more fine-grained understanding of historical climate patterns and their relationship to sea level. As climate change looms, that could prove to be quite useful in our own precarious moment.